Cartridge type electric fuse



E. JACKS ET AL CARTRIDGE TYPE ELECTRIC FUSE June -l7, 1969 Filed Dec. 7, 1966 Sheet Z Of 2 ATTORNEYS June 17, 1969 JACKS ET AL CARTRIDGE TYPE ELECTRIC FUSE Filed Dec. 7, 1966 \y WWOB United States Patent T U.S. Cl. 337-249 4 Claims ABSTRACT OF THE DISCLOSURE A fuse link having a sealed housing enclosing a number of fusible elements, and valve means for exhausting to atmosphere any gases which are developed within the housing and which exert a pressure exceeding a predetermined value.

This invention relates to fuse links.

From one aspect, the present invention consists in a fuse link comprising a sealed housing enclosing one or more fusible elements, and valve means for exhausting to atmosphere any gases within said housing the pressure of which exceeds a predetermined value.

In particular, the valve means is designed to exhaust gases the pressure of which rises under the influence of heat developed upon the fusible element rupturing in response to the passage therethrough of an excessively high and severe current, e.g. under short circuit conditions, the gases being exhausted along a path the dimensions of which are sufficient substantially to deionise these gases before they are emitted to atmosphere.

Accordingly, this invention is concerned with the manufacture of fuse links which are able to sustain the high internal pressures which may develop upon the conduction of high currents under, for example, severe short circuit conditions, and by incorporating the valve means the walls of the fuse link may be formed with a thinner gauge material than has been necessary before, since the pressure which these walls need now withstand is limited to the aforesaid predetermined value.

The danger of the fuse link exploding under such conditions is therefore no greater than conventional fuses which do not employ such pressure relief means, and by ensuring that the gases are deionised by exhausting them through a long path before they are emitted to atmosphere, the fuse link can be used under the same conditions and in the same environment as conventional fuses.

The invention is particularly, but not exclusively, applicable to highly-rated fuses, i.e. fuses rated at 1000 amps. or more, since the problems which this invention is designed to solve become more acute with such fuses.

In order that the invention may be fully understood, one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a fuse link according to this invention;

FIGURE 2 is an axial section through an end part of the fuse link shown in FIGURE 1;

FIGURE 3 is a sectional plan view through the lines Y-Y in FIGURE 2; and

FIGURE 4 is a part-axial section through the fuse link shown in FIGURE 2 under different conditions of operation from those shown in that figure.

Refering now to FIGURES 1 to 3, the fuse link cornprises two copper end caps 1 and 2 comprising a knife blade contact and a disc between which is located a hollow cylindrical body 3. The body 3 is secured to these 3,451,025 Patented June 17, 1969 caps both by frictional engagement and by a plurality of radially extending screws 4, the end surfaces of these caps, together with the adjoining surfaces of the body, being covered by flexible shrouds 5, e.g. nylon, which also conceal the heads of the screws.

The body 3 may conveniently be fabricated in the form of superposed integral laminations, the interior surface wall portion being formed in a silicon resin bonded mica (with a low content of bonding resin in order to reduce the risk of internal tracking occurring due to carbonisation) and the remaining portion being silicon bonded fiberglass. In particular, this body may conveniently be the same as that described in our co-pending patent application No. 51796 of 1965. Alternatively, the body 3 may Wholly comprise a melamine resin-bonded fiberglass.

The end caps are secured in the body 3 through the intermediary of a cup-shaped annular ring 6 and a number, e.g. three, of L-shaped copper spaces 7 equidistantly disposed around the extenal periphery of this ring, these spacers serving both to centre the caps within the cylindrical body 3 and space the caps therefrom.

An annular recess is formed in the outer surfaces of this ring 6 to accommodate a resilient band 8, e.g. silicone-rubber, which is inwardly compressed by, and bears against, the inner wall of the body 3. In addition, the ring 6 has an outwardly extending lip 9 which overlaps the end of the body 3, and an inwardly extending lip 10 which serves as a support for a number of highrupturing-current silver strip fuse elements 11.

In particular, these fuse elements are supported in a number of radially extending slots 12 formed in the lip 10, (these elements may be of the type, and manufactured by the method, described in our co-pending patent application No. 28,654 of 1963, for example), and by disposing these strip elements in radial planes it is ensured that the greatest possible spacing is obtained between adjacent elements located along a circle of any desired radius.

In the assembly of this device, the silicone-rubber band 8 is first slipped into the recess in the ring '6 and two of these rings are forced into the opposite ends of the body 3. The external diameter of each ring is such that it is freely spaced from the inner diameter of the body 3, the body compressing and sliding over the band 8, whose edges may conveniently be tapered, and being forced tightly over the soft-metal-spacers 7, the leading edges of which may also be inwardly tapered to assist this action. Accordingly, the ring 6 is housed tightly within the body 3, it being spaced radially from the inner walls of this body, and axially from the end walls, by the thickness of the L-shaped spacers 7.

After the fuse elements 11 have been located in the radial slots 12 and their protruding ends bent over and soldered to the exterior surfaces of the lips 10, the end caps 1 and 2 are forced into the rings and the screws 4 are fastened in position so as to clamp the assembly tightly together. Finally, the flexible shrouds 5 are fitted over the ends.

In operation, upon low over current or moderate short circuit conditions, rupture of the fuse elements is such that the resulting pressure built up of ionised gases within the fuse link is insufficient to disturb the sealing bands 8. However, when the fuse link is subjected to a severe short-circuit, and a high pressure is consequently built up, the internal pressure rises until it overcomes the sealing pressure of the or each band and the high pressure gases leak past this band and force away the associated shroud 5 to exhaust to atmosphere, as shown in FIGURE 4. The width of the gap, and the length of the path, through which these gases travel, are so dimen- 3 sioned as to ensure that these gases are effectively deionised before they are emitted to atmosphere.

Accordingly, this fuse link is designed so as to incorporate a safety valve" including a gas deionisation zone, so as to restrict the pressures which the walls of the fuse link need sustain, and this enables the body 3 of the fuse link to be made with thinner walls than has been possible before with fuses of comparable ratings.

This feature is particularly advantageous with high rating fuse links, e.g. high-rupturing-current fuses rated at 1600 amps.

We claim:

1. A sealed electric fuse link comprising 1 an elongated tubular body of insulating material,

two metal end caps carried by the tubular body and supporting between them a plurality of fusible elements, at least one of the metal end caps comprising a knife blade contact and an inner disc,

a ring embracing said inner disc and'having an outwardly extending lip on one end overlapping the adjacent end of the tubular body, and

an inwardly extending lip on the other end providing a support for said fusible elements,

spacer means connected between the ring on each metal end cap and the inner wall of the tubular body to define a passage between said cap and the body, and

valve means comprising a compressible band means for exhausting to atmosphere any gases from within said sealed fuse link, the pressure of which exceeds a predetermined value, said valve means further compl'lSlllg a flexible member disposed over the end cap and the tubular body and normally operable to seal the said passage defined by the spacer means.

2. A fuse link according to claim 1, wherein said compressible band is disposed between the end cap and the tubular body and normally operable to seal the said passage.

3. A fuse link according to claim 2, wherein the tubular body comprises a melamine resin-bonded fibreglass.

4. A sealed fuse link comprising i an elongated tubular body of insulating material,

two metal end caps carried by the tubular body and supporting between them a plurality of fusible elements,

spacer means connected between at least one of the end caps and the inner wall of the tubular body to define a passage between the cap and the body, and

valve means for exhausting any gases from within said sealed fuse link the pressure of which exceeds a predetermined value, said valve' means comprising an internal compressible member mounted adjacent said spacer means and connected between the end cap and the inner Wall of the tubular body and norm-ally operable to seal the said passage, and

an external flexible member disposed over the end cap and the tubular body and normally operable to seal the said passage, both the first and the second members being distorted in response to the pressure of gases within the housing exceeding said predetermined value to exhaust them to atmosphere.

References Cited UNITED STATES PATENTS 1,857,298 5/1932 Fogal 200-132 3,080,463 5/ 1963 Kozacka 200- 3,217,126 11/1965 Smith et a1. 200-132 1,484,058 2/ 1924 Buchanan 337-250 1,506,049 8/1924 Condit 337-250 1,562,494 11/1925 Conant 337-250 1,674,633 6/1928 Bowen 337-250 X 2,647,970 8/1953 Edsall et al. 337-248 X 2,650,283 8/1953 Von Hoorn 337-250 2,953,665 9/1960 Cox 337-248 2,837,614 6/1958 Fister 337-164 X BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

US. Cl. X.R. 337-250 

